The present invention relates to rotary placers used for the feeding of labels, cartons and related products. In particular, this invention relates to a rotary transfer device having a servo motor for varying the rotational movement of an article transfer mechanism.
Typical rotary transfer devices include a rotating main body and arms which rotate on centers radially disposed around the center line of the rotating main body. Each arm is equipped with picking and holding devices. Rotation of the arms is normally controlled by gearing or by belts. The picking devices normally travel through at least two phases: a picking phase and a placing phase. During the picking phase, the article transfer mechanism picks up an article from a feeder or other fixed point. During the placing phase, the article transfer mechanism places the article in a new location, such as on a package.
An example of such a rotary transfer device is disclosed in U.S. Pat. No. 4,530,686, entitled "ROTARY PACKAGING TECHNOLOGY." With this rotary transfer device, the arms are coupled to planetary gears which rotate about relative to a stationary center or sun gear. The ratio of the stationary sun gear to the planet gear, which rotates about the sun gear in the main body, imparts a secondary rotating motion to the arms. Gripping devices are mounted to the end of the arms. The value of the ratio between the sizes of the planet gear and the sun gear and the length of the arms determines the path or the profile of an end gripping device.
Typically, as shown by U.S. Pat. No. 4,530,686, the arrangement of ratios and arm lengths is established so that the gripping device travels through two or three fixed point apex locations in the cycloidal motion of the gripper device. As the gripper device or cup approaches each fixed point, there is little radial travel about the main rotating body axis or center line. However, a large amount of travel on a linear axis from the main body center toward the fixed point exists. As the main body continues to rotate, the gripper device retracts along a similar path.
This type of motion profile, a fixed-point profile, is commonly used because it facilitates picking up an object or article from a stationary feeding system or picking station and placing the article at a fixed point. Although the motion profile appears to stop at fixed points, the profile is actually comprised of rotary paths. As a result, the gripping device travels in one rotational direction at a constant rate. Because of the constant direction and rate, this type of rotary transfer device is well-suited for high speeds.
Although such a rotary transfer device is well-suited to picking up and placing at fixed points, rotary transfer devices employing stationary center gears are less than ideal where the object that the article is to be placed on is moving. The problem occurs because there is a difference in the relative motion during the placing phase between the gripping device and the object. The greater the pitch or spacing between products and the relative product travel during the placing phase, the worse the problem. Although the fixed-point motion profile of the gripping device could be altered to better coordinate the relative motions of the gripper device and the moving object, the altered motion profile would also be created at the picking station where the fixed-point profile is required.
Thus, the placement of articles such as coupons or labels to or on moving objects, such as packages encounters several problems. The relative movement between the individual article and the moving object causes inherent placement difficulties and damage. This problem is accentuated in high-speed placement operations.
In an attempt to solve this problem, U.S. Pat. No. 4,901,843, entitled "ADVANCING MOTION ROTARY APPARATUS" discloses a rotary transfer device having a timed and intermittently reciprocating center gear. With this device, the center gear is reciprocated clockwise, and then counterclockwise to accelerate the rotational movement of the gripping device at its apex to cause the gripping device to travel at the same speed as the moving object, i.e., a placing profile, during the placing phase. The reciprocating or oscillating motion of the center gear is created by a cam and a linkage mechanism communicating between the cam and the center gear. Movement of the center gear is controlled by the cam timed to the rotating main body so as to retard and advance the gripper device during the placing phase.
During the picking phase, the center gear is stationary while the planetary gear rotates about the center gear. Because the planetary gear has a radius one-half the radius of the center gear (a mechanical 2:1 gearing ratio), the planetary gear and the gripper device complete two full rotations for every single rotation of the rotating main body. During the picking phase, the center gear of this device operates almost identical to the device described in U.S. Pat. No. 4,530,686.
Several disadvantages are also associated with this rotary transfer device. For example, when the pitch or frequency of the moving objects changes, the placing profile must also be changed. To change the placing profile, the cam must be physically removed and replaced. In addition, because the cam and the center gear must reciprocate, that is, move in one direction, stop, and reverse direction, the rotary transfer device requires more energy to overcome inertia involved in stopping and starting a mass. Consequently, the motion profile is not as smooth as continuous motion in one direction. Moreover, because of the reciprocating nature of this rotary transfer device, high-speed performance is compromised or is limited.